The invention relates to a photopolymerizable composition comprising a polymeric binder, an ethylenically unsaturated compound which can be polymerized by free radicals and a photoinitiator. The invention further relates to a photopolymerizable recording material comprised of a support layer and a photopolymerizable layer comprising the above-indicated photopolymerizable composition. The compositions and materials of the invention are useful in the production of printing plates, relief images and photoresists.
A great number of photoinitiators have been disclosed in the patent literature. Examples of these are benzophenone, 4,4'-bis-dialkylamino-benzophenones, anthraquinones, thioxanthone derivatives, benzoins, benzoin ethers, 2,4,5-triarylimidazolyl dimers, acridine, phenazine and quinoline derivatives and trichloromethyl compounds, in particular trichloromethyl-s-triazines.
Combinations of two or more photoinitiators have also been described, for example, combinations of 4,4'-bis-dialkylamino-benzophenone with benzophenone or other compounds, combinations of benzoylmethylene-N-alkyl-naphthothiazoline and trihalomethyl triazines, combinations of a 2,4,5-triarylimidazolyl dimer and a p-aminophenylketone, combinations of dimethylthioxanthone and 4-dialkylamino-benzoates (see JP-A 82/23602), combinations of N-heterocyclic compounds, in particular acridine compounds, with compounds containing trichloromethyl groups (see EP-A 243 784) and combinations of these latter two components and photoreducible dyes (see EP-A 287,817).
DE-A 35 03 113 describes acylhaloacetic acid amide derivatives and mixtures of these photoinitiators with 4,4'-bis-dialkylamino-benzophenones, benzophenone derivatives or cyclic ketones. U.S. Pat. No. 3,661,588 discloses mixtures of photoinitiators comprising a p-aminophenyl ketone and an active methylene or amino compound. A mixture of N-phenylacridone and trihalomethyl compounds is described in DE-A 26 10 842.
Ternary photoinitiator systems have also been disclosed, for example, a mixture comprising a 4,4'-bis-dialkylamino-benzophenone, a benzophenone derivative and a compound containing a trihalomethyl group is described in DE-A 33 39 228.
An important field of application of compositions of this type is the preparation of dry resist materials. In this application, photoresist layers are used which have a thickness of the order of about 10 to about 100 .mu.m. It is therefore essential that the side walls of the developed resist lines extend as far as possible in a vertical direction so that the line covered on the substrate, for example, on the circuit board, corresponds as close as possible to the artwork used. Dry resists should therefore meet, in particular, the following three requirements:
1. High photosensitivity PA1 2. High resolution PA1 3. Vertical side wall configuration PA1 a) a polymeric binder, PA1 b) a compound which can be polymerized by free radicals and has at least one terminal ethylenic double bond, PA1 c) an N-heterocyclic compound effective as a photoinitiator, PA1 d) a thioxanthone derivative which acts as a photoinitiator of the formula I ##STR1## and e) a dialkylamino compound which acts as a photoinitiator of one of the formulae II or III ##STR2## in which R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are independently selected from hydrogen or halogen atoms or alkyl, alkoxy, carboxyl, alkoxycarbonyl or aryloxycarbonyl groups, PA1 R.sup.12 is a hydrogen atom, an alkyl, aryl, aralkyl or aralkenyl group, PA1 R.sup.13 and R.sup.14 are identical or different and denote hydrogen or halogen atoms, alkyl or alkoxy groups, PA1 n is 0 or 1 and PA1 m is 1 or 2.
Although it has been possible to substantially increase photosensitivity by means of the known photoinitiator combinations, it has hitherto been impossible to at the same time improve the other two characteristics. As a general rule, high photosensitivity causes a positive side wall configuration, i.e. the resist line produced is wider at the base than at the upper edge. A positive or negative side wall configuration, in turn, results in impaired resolution.